As of July 2013[update], the Google Play store has had over one million Android applications ("apps") published, and over 50 billion applications downloaded.[11] A developer survey conducted in April–May 2013 found that 71% of mobile developers develop for Android.[12] At Google I/O 2014, the company revealed that there were over one billion active monthly Android users, up from 538 million in June 2013.[13] As of 2015[update], Android has the largest installed base of all general-purpose operating systems.

Android's source code is released by Google under open source licenses, although most Android devices ultimately ship with a combination of open source and proprietary software, including proprietary software developed and licensed by Google.[3] Initially developed by Android, Inc., which Google backed financially and later bought in 2005,[14] Android was unveiled in 2007, along with the founding of the Open Handset Alliance—​a consortium of hardware, software, and telecommunication companies devoted to advancing open standards for mobile devices.[15]

Android is popular with technology companies which require a ready-made, low-cost and customizable operating system for high-tech devices.[16] Android's open nature has encouraged a large community of developers and enthusiasts to use the open-source code as a foundation for community-driven projects, which add new features for advanced users[17] or bring Android to devices which were officially released running other operating systems. The operating system's success has made it a target for patent litigation as part of the so-called "smartphone wars" between technology companies.[18][19]

History

Android, Inc. was founded in Palo Alto, California in October 2003 by Andy Rubin (co-founder of Danger),[20]Rich Miner (co-founder of Wildfire Communications, Inc.),[21] Nick Sears (once VP at T-Mobile),[22] and Chris White (headed design and interface development at WebTV[14]) to develop, in Rubin's words, "smarter mobile devices that are more aware of its owner's location and preferences".[14] The early intentions of the company were to develop an advanced operating system for digital cameras. Though, when it was realized that the market for the devices was not large enough, the company diverted its efforts toward producing a smartphone operating system that would rival Symbian and Microsoft Windows Mobile.[23] Despite the past accomplishments of the founders and early employees, Android Inc. operated secretly, revealing only that it was working on software for mobile phones.[14] That same year, Rubin ran out of money. Steve Perlman, a close friend of Rubin, brought him $10,000 in cash in an envelope and refused a stake in the company.[24]

Google acquired Android Inc. on August 17, 2005; key employees of Android Inc., including Rubin, Miner, and White, stayed at the company after the acquisition.[14] Not much was known about Android Inc. at the time, but many assumed that Google was planning to enter the mobile phone market with this move.[14] At Google, the team led by Rubin developed a mobile device platform powered by the Linux kernel. Google marketed the platform to handset makers and carriers on the promise of providing a flexible, upgradable system. Google had lined up a series of hardware component and software partners and signaled to carriers that it was open to various degrees of cooperation on their part.[25][26][27]

Speculation about Google's intention to enter the mobile communications market continued to build through December 2006.[28] An earlier prototype codenamed "Sooner" had a closer resemblance to a BlackBerry phone, with no touchscreen, and a physical, QWERTY keyboard, but was later re-engineered to support a touchscreen, to compete with other announced devices such as the 2006 LG Prada and 2007 Apple iPhone.[29][30] In September 2007, InformationWeek covered an Evalueserve study reporting that Google had filed several patent applications in the area of mobile telephony.[31][32]

In 2010, Google launched its Nexus series of devices – a line of smartphones and tablets running the Android operating system, and built by manufacturing partners. HTC collaborated with Google to release the first Nexus smartphone,[35] the Nexus One. Google has since updated the series with newer devices, such as the Nexus 5 phone (made by LG) and the Nexus 7 tablet (made by Asus). Google releases the Nexus phones and tablets to act as their flagship Android devices, demonstrating Android's latest software and hardware features. Until January 2015, Google offered several Google Play Edition devices over Google Play, as Google-customized Android phones and tablets that, while not carrying the Google Nexus branding, run an unmodified version of Android.

On March 13, 2013 Larry Page announced in a blog post that Andy Rubin had moved from the Android division to take on new projects at Google.[36] He was replaced by Sundar Pichai, who also continues his role as the head of Google's Chrome division,[37] which develops Chrome OS.

Since 2008, Android has seen numerous updates which have incrementally improved the operating system, adding new features and fixing bugs in previous releases. Each major release is named in alphabetical order after a dessert or sugary treat; for example, version 1.5 "Cupcake" was followed by 1.6 "Donut". Version 4.4.4 "KitKat" appeared as a security-only update; it was released on June 19, 2014, shortly after 4.4.3 was released.[38][39] Android 5.0 "Lollipop" was released on November 14, 2014, introducing "material design" as a new design language and one if its key new features; it was followed by two bugfix releases (5.0.1 and 5.0.2). [40]

In 2014, Google launched Android One, a standardized smartphone, mainly targeting customers in the developing world. Android One smartphones running the latest version of Android (e.g. the latest Android 5.1) close to the stock version of the operating system. As of March 3, 2015[update], the newest version of the Android operating system, 5.1, is available for selected devices including the Android One series, the Nexus 6 phablet, and the Nexus 9 tablet.[41]

From 2010 to 2013, Hugo Barra served as product spokesperson for the Android team, representing Android at both press conferences and Google I/O, Google’s annual developer-focused conference. Barra's product involvement included the entire Android ecosystem of software and hardware, including Honeycomb, Ice Cream Sandwich, Jelly Bean and KitKat operating system launches, the Nexus 4 and Nexus 5 smartphones, the Nexus 7[42] and Nexus 10 tablets,[43] and other related products such as Google Now[44] and Google Voice Search, Google’s speech recognition product comparable to Apple’s Siri.[44] In 2013, Barra left the Android team for Chinese smartphone maker Xiaomi.[45]

Features

Interface

Notifications are accessed by sliding from the top of the display; individual notifications can be dismissed by sliding them away, and may contain additional functions (such as on the "missed call" notification seen here).

Android's default user interface is based on direct manipulation,[46] using touch inputs, that loosely correspond to real-world actions, like swiping, tapping, pinching, and reverse pinching to manipulate on-screen objects, and a virtual keyboard.[46] The response to user input is designed to be immediate and provides a fluid touch interface, often using the vibration capabilities of the device to provide haptic feedback to the user. Internal hardware such as accelerometers, gyroscopes and proximity sensors[47] are used by some applications to respond to additional user actions, for example adjusting the screen from portrait to landscape depending on how the device is oriented, or allowing the user to steer a vehicle in a racing game by rotating the device, simulating control of a steering wheel.[48]

Android devices boot to the homescreen, the primary navigation and information point on the device, which is similar to the desktop found on PCs. Android homescreens are typically made up of app icons and widgets; app icons launch the associated app, whereas widgets display live, auto-updating content such as the weather forecast, the user's email inbox, or a news ticker directly on the homescreen.[49] A homescreen may be made up of several pages that the user can swipe back and forth between, though Android's homescreen interface is heavily customisable, allowing the user to adjust the look and feel of the device to their tastes.[50] Third-party apps available on Google Play and other app stores can extensively re-theme the homescreen, and even mimic the look of other operating systems, such as Windows Phone.[51] Most manufacturers, and some wireless carriers, customise the look and feel of their Android devices to differentiate themselves from their competitors.[52]

Present along the top of the screen is a status bar, showing information about the device and its connectivity. This status bar can be "pulled" down to reveal a notification screen where apps display important information or updates, such as a newly received email or SMS text, in a way that does not immediately interrupt or inconvenience the user.[53] Notifications are persistent until read (by tapping, which opens the relevant app) or dismissed by sliding it off the screen. Beginning on Android 4.1, "expanded notifications" can display expanded details or additional functionality; for instance, a music player can display playback controls, and a "missed call" notification provides buttons for calling back or sending the caller an SMS message.[54]

Android provides the ability to run applications which change the default launcher and hence the appearance and externally visible behaviour of Android. These appearance changes include a multi-page dock or no dock, and many more changes to fundamental features of the user interface.[55]

Android has a growing selection of third-party applications, which can be acquired by users by downloading and installing the application's APK file, or by downloading them using an application store program that allows users to install, update, and remove applications from their devices. Google Play Store is the primary application store installed on Android devices that comply with Google's compatibility requirements and license the Google Mobile Services software.[3][59] Google Play Store allows users to browse, download and update applications published by Google and third-party developers; As of July 2013[update], there are more than one million applications available for Android in Play Store.[60] As of May 2013[update], 48 billion applications have been installed from Google Play Store[61] and in July 2013, 50 billion applications were installed.[62][63] Some carriers offer direct carrier billing for Google Play application purchases, where the cost of the application is added to the user's monthly bill.[64]

Due to the open nature of Android, a number of third-party application marketplace also exist for Android, either to provide a substitute for devices that are not allowed to ship with Google Play Store, provide applications that cannot be offered on Google Play Store due to policy violations, or for other reasons. Examples of these third-party stores have included the Amazon Appstore, GetJar, and SlideMe. F-Droid, another alternative marketplace, seeks to only provide applications that are distributed under free and open sourcelicenses.[3][65][66][67]

Memory management

Since Android devices are usually battery-powered, Android is designed to manage memory (RAM) to keep power consumption at a minimum, in contrast to desktop operating systems which generally assume they are connected to unlimited mains electricity. When an Android application is no longer in use, the system will automatically suspend it in memory; while the application is still technically "open", suspended applications consume no resources (for example, battery power or processing power) and sit idly in the background until needed again. This brings a dual benefit by increasing the general responsiveness of Android devices, since applications do not need to be closed and reopened from scratch each time, and by ensuring that background applications do not consume power needlessly.[68][69]

Android manages the applications stored in memory automatically: when memory is low, the system will begin killing applications and processes that have been inactive for a while, in reverse order since they were last used (oldest first). This process is designed to be invisible to the user, so that users do not need to manage memory or the killing of applications themselves.[70][71] As of 2011, third-party task killers were reported by Lifehacker as doing more harm than good.[72]

Hardware

The main hardware platform for Android is the ARM architecture (ARMv7 and ARMv8-A architectures), with x86 and MIPS architectures also officially supported (the latter two became officially supported in later Android versions). Since Android 5.0 "Lollipop", 64-bit variants of all platforms are supported in addition to the 32-bit variants.[73] Unofficial Android-x86 project used to provide support for the x86 and MIPS architectures ahead of the official support.[5][74] Since 2012, Android devices with Intel processors began to appear, including phones[75] and tablets. While gaining support for 64-bit platforms, Android was first made to run on 64-bit x86 and then on ARM64.

As of November 2013[update], Android 4.4 recommends at least 512 MB of RAM,[76] while for "low RAM" devices 340 MB is the required minimum amount that does not include memory dedicated to various hardware components such as the baseband processor.[77] Android 4.4 requires a 32-bitARMv7, MIPS or x86 architecture processor (latter two through unofficial ports),[5][78] together with an OpenGL ES 2.0 compatible graphics processing unit (GPU).[79] Android supports OpenGL ES 1.1, 2.0, 3.0 and 3.1. Some applications may explicitly require a certain version of the OpenGL ES, and suitable GPU hardware is required to run such applications.[79]

Android devices incorporate many optional hardware components, including still or video cameras, GPS, orientation sensors, dedicated gaming controls, accelerometers, gyroscopes, barometers, magnetometers, proximity sensors, pressure sensors, thermometers, and touchscreens. Some hardware components are not required, but became standard in certain classes of devices, such as smartphones, and additional requirements apply if they are present. Some other hardware was initially required, but those requirements have been relaxed or eliminated altogether. For example, as Android was developed initially as a phone OS, hardware such as microphones were required, while over time the phone function became optional.[63] Android used to require an autofocus camera, which was relaxed to a fixed-focus camera[63] if it is even present at all, since the camera was dropped as a requirement entirely when Android started to be used on set-top boxes.

In addition to running on smartphones and tablets, several vendors run Android natively on regular PC hardware with a keyboard and mouse.[80][81][82] In addition to their availability on commercially available hardware, similar PC hardware–friendly versions of Android are freely available from the Android-x86 project, including customized Android 4.4.[83] Using the Android emulator that is part of the Android SDK, or by using BlueStacks or Andy, Android can also run non-natively on x86.[84][85] Chinese companies are building a PC and mobile operating system, based on Android, to "compete directly with Microsoft Windows and Google Android".[86] The Chinese Academy of Engineering noted that "more than a dozen" companies were customising Android following a Chinese ban on the use of Windows 8 on government PCs.[87][88][89]

Development

Android green figure, next to its original packaging.

Android is developed in private by Google until the latest changes and updates are ready to be released, at which point the source code is made available publicly.[90] This source code will only run without modification on select devices, usually the Nexus series of devices. The source code is, in turn, adapted by OEMs to run on their hardware.[91] Android's source code does not contain the often proprietary device drivers that are needed for certain hardware components.[92]

The green Android logo was designed for Google in 2007 by graphic designer Irina Blok. The design team was tasked with a project to create a universally identifiable icon with the specific inclusion of a robot in the final design. After numerous design developments based on science-fiction and space movies, the team eventually sought inspiration from the human symbol on restroom doors and modified the figure into a robot shape. As Android is open-sourced, it was agreed that the logo should be likewise, and since its launch the green logo has been reinterpreted into countless variations on the original design.[93]

Update schedule

Google provides major incremental upgrades to Android every six to nine months, with confectionery-themed names, which most devices are capable of receiving over the air.[94] The latest major release is Android 5.0 "Lollipop".[40]

Compared to its chief rival mobile operating system, namely iOS, Android updates are typically slow to reach actual devices. For devices not under the Nexus brand, updates often arrive months from the time the given version is officially released.[95] This is partly due to the extensive variation in hardware of Android devices, to which each upgrade must be specifically tailored, as the official Google source code only runs on their flagship Nexus devices. Porting Android to specific hardware is a time- and resource-consuming process for device manufacturers, who prioritize their newest devices and often leave older ones behind.[95] Hence, older smartphones are frequently not updated if the manufacturer decides it is not worth their time, regardless of whether the phone is capable of running the update. This problem is compounded when manufacturers customize Android with their own interface and apps, which must be reapplied to each new release. Additional delays can be introduced by wireless carriers who, after receiving updates from manufacturers, further customize and brand Android to their needs and conduct extensive testing on their networks before sending the upgrade out to users.[95]

The lack of after-sale support from manufacturers and carriers has been widely criticized by consumer groups and the technology media.[96][97] Some commentators have noted that the industry has a financial incentive not to upgrade their devices, as the lack of updates for existing devices fuels the purchase of newer ones,[98] an attitude described as "insulting".[97]The Guardian has complained that the method of distribution for updates is complicated only because manufacturers and carriers have designed it that way.[97] In 2011, Google partnered with a number of industry players to announce an "Android Update Alliance", pledging to deliver timely updates for every device for 18 months after its release;[99] however, there has not been another official word about that alliance.[95][100]

In 2012, Google began decoupling certain aspects of the operating system (particularly core applications) so they could be updated through Google Play Store, independently of Android itself. One of these components, Google Play Services, is a closed-source system-level process providing APIs for Google services, installed automatically on nearly all devices running Android version 2.2 and higher. With these changes, Google can add new operating system functionality through Play Services and application updates without having to distribute an upgrade to the operating system itself. As a result, Android 4.2 and 4.3 contained relatively fewer user-facing changes, focusing more on minor changes and platform improvements.[3][101]

Linux kernel

Android's kernel is based on one of the Linux kernel's long-term support (LTS) branches. Since April 2014, Android devices mainly use versions 3.4 or 3.10 of the Linux kernel.[102][103] The specific kernel version depends on the actual Android device and its hardware platform;[104][105][106] Android has used various kernel versions since the version 2.6.25 that was used in Android 1.0.[33]

Android's variant of the Linux kernel has further architectural changes that are implemented by Google outside the typical Linux kernel development cycle, such as the inclusion of components like Binder, ashmem, pmem, logger, wakelocks, and different out-of-memory (OOM) handling.[107][108][109] Certain features that Google contributed back to the Linux kernel, notably a power management feature called "wakelocks", were rejected by mainline kernel developers partly because they felt that Google did not show any intent to maintain its own code.[110][111][112] Google announced in April 2010 that they would hire two employees to work with the Linux kernel community,[113] but Greg Kroah-Hartman, the current Linux kernel maintainer for the stable branch, said in December 2010 that he was concerned that Google was no longer trying to get their code changes included in mainstream Linux.[111] Some Google Android developers hinted that "the Android team was getting fed up with the process," because they were a small team and had more urgent work to do on Android.[114]

In August 2011, Linus Torvalds said that "eventually Android and Linux would come back to a common kernel, but it will probably not be for four to five years".[115] In December 2011, Greg Kroah-Hartman announced the start of Android Mainlining Project, which aims to put some Android drivers, patches and features back into the Linux kernel, starting in Linux 3.3.[116] Linux included the autosleep and wakelocks capabilities in the 3.5 kernel, after many previous attempts at merger. The interfaces are the same but the upstream Linux implementation allows for two different suspend modes: to memory (the traditional suspend that Android uses), and to disk (hibernate, as it is known on the desktop).[117] Google maintains a public code repository that contains their experimental work to re-base Android off the latest stable Linux versions.[118][119]

The flash storage on Android devices is split into several partitions, such as /system for the operating system itself, and /data for user data and application installations.[120] In contrast to desktop Linux distributions, Android device owners are not given root access to the operating system and sensitive partitions such as /system are read-only. However, root access can be obtained by exploiting security flaws in Android, which is used frequently by the open-source community to enhance the capabilities of their devices,[121] but also by malicious parties to install viruses and malware.[122]

Android's standard C library, Bionic, was developed by Google specifically for Android, as a derivation of the BSD's standard C library code. Bionic itself has been designed with several major features specific to the Linux kernel. The main benefits of using Bionic instead of the GNU C Library (glibc) or uClibc are its smaller runtime footprint, and optimization for low-frequency CPUs. At the same time, Bionic is licensed under the terms of BSD licence, which Google finds more suitable for the Android's overall licensing model.[130]

Aiming for a different licensing model, toward the end of 2012 Google switched the Bluetooth stack in Android from the GPL-licensed BlueZ to the Apache-licensed BlueDroid.[132]

Android does not have a native X Window System by default, nor does it support the full set of standard GNU libraries. This made it difficult to port existing Linux applications or libraries to Android,[127] until version r5 of the Android Native Development Kit brought support for applications written completely in C or C++.[133] Libraries written in C may also be used in applications by injection of a small shim and usage of the JNI.[134]

Open-source community

Android has an active community of developers and enthusiasts who use the Android Open Source Project (AOSP) source code to develop and distribute their own modified versions of the operating system.[135] These community-developed releases often bring new features and updates to devices faster than through the official manufacturer/carrier channels, albeit without as extensive testing or quality assurance;[17] provide continued support for older devices that no longer receive official updates; or bring Android to devices that were officially released running other operating systems, such as the HP TouchPad. Community releases often come pre-rooted and contain modifications unsuitable for non-technical users, such as the ability to overclock or over/undervolt the device's processor.[136]CyanogenMod is the most widely used community firmware,[137] and acts as a foundation for numerous others.

Historically, device manufacturers and mobile carriers have typically been unsupportive of third-party firmware development. Manufacturers express concern about improper functioning of devices running unofficial software and the support costs resulting from this.[138] Moreover, modified firmwares such as CyanogenMod sometimes offer features, such as tethering, for which carriers would otherwise charge a premium. As a result, technical obstacles including locked bootloaders and restricted access to root permissions are common in many devices. However, as community-developed software has grown more popular, and following a statement by the Librarian of Congress in the United States that permits the "jailbreaking" of mobile devices,[139] manufacturers and carriers have softened their position regarding third party development, with some, including HTC,[138]Motorola,[140]Samsung[141][142] and Sony,[143] providing support and encouraging development. As a result of this, over time the need to circumvent hardware restrictions to install unofficial firmware has lessened as an increasing number of devices are shipped with unlocked or unlockable bootloaders, similar to Nexus series of phones, although usually requiring that users waive their devices' warranties to do so.[138] However, despite manufacturer acceptance, some carriers in the US still require that phones are locked down, frustrating developers and customers.[144][144]

Security and privacy

Permissions are used to control a particular application's access to system functions.

Android applications run in a sandbox, an isolated area of the system that does not have access to the rest of the system's resources, unless access permissions are explicitly granted by the user when the application is installed. Before installing an application, Play Store displays all required permissions: a game may need to enable vibration or save data to an SD card, for example, but should not need to read SMS messages or access the phonebook. After reviewing these permissions, the user can choose to accept or refuse them, installing the application only if they accept.[145] The sandboxing and permissions system lessens the impact of vulnerabilities and bugs in applications, but developer confusion and limited documentation has resulted in applications routinely requesting unnecessary permissions, reducing its effectiveness.[146] Google has now pushed an update to Android Verify Apps feature, which will now run in background to detect malicious processes and crack them down.[147]

The "App Ops" privacy and application permissions control system, used for internal development and testing by Google, was introduced in Google's Android 4.3 release for the Nexus devices. Initially hidden, the feature was discovered publicly; it allowed users to install a management application and approve or deny permission requests individually for each of the applications installed on a device.[148] Access to the App Ops was later restricted by Google starting with Android 4.4.2 with an explanation that the feature was accidentally enabled and not intended for end-users; for such a decision, Google received criticism from the Electronic Frontier Foundation.[149][150][151] Individual application permissions management, through the App Ops or third-party tools, is currently only possible with root access to the device.[152][153]

Research from security company Trend Micro lists premium service abuse as the most common type of Android malware, where text messages are sent from infected phones to premium-rate telephone numbers without the consent or even knowledge of the user.[154] Other malware displays unwanted and intrusive adverts on the device, or sends personal information to unauthorised third parties.[154] Security threats on Android are reportedly growing exponentially; however, Google engineers have argued that the malware and virus threat on Android is being exaggerated by security companies for commercial reasons,[155][156] and have accused the security industry of playing on fears to sell virus protection software to users.[155] Google maintains that dangerous malware is actually extremely rare,[156] and a survey conducted by F-Secure showed that only 0.5% of Android malware reported had come from the Google Play store.[157]

Google currently uses Google Bouncer malware scanner to watch over and scan the Google Play store apps.[158] It is intended to flag up suspicious apps and warn users of any potential threat with an application before they download it.[159] Android version 4.2 Jelly Bean was released in 2012 with enhanced security features, including a malware scanner built into the system, which works in combination with Google Play but can scan apps installed from third party sources as well, and an alert system which notifies the user when an app tries to send a premium-rate text message, blocking the message unless the user explicitly authorises it.[160] Several security firms, such as Lookout Mobile Security,[161]AVG Technologies,[162] and McAfee,[163] have released antivirus software for Android devices. This software is ineffective as sandboxing also applies to such applications, limiting their ability to scan the deeper system for threats.[164][165]

Android smartphones have the ability to report the location of Wi-Fi access points, encountered as phone users move around, to build databases containing the physical locations of hundreds of millions of such access points. These databases form electronic maps to locate smartphones, allowing them to run apps like Foursquare, Google Latitude, Facebook Places, and to deliver location-based ads.[166] Third party monitoring software such as TaintDroid,[167] an academic research-funded project, can, in some cases, detect when personal information is being sent from applications to remote servers.[168] In August 2013, Google released Android Device Manager (ADM), a component that allows users to remotely track, locate, and wipe their Android device through a web interface.[101][169] In December 2013, Google released ADM as an Android application on the Google Play store, where it is available to devices running Android version 2.2 and higher.[170][171]

The open-source nature of Android allows security contractors to take existing devices and adapt them for highly secure uses. For example Samsung has worked with General Dynamics through their Open Kernel Labs acquisition to rebuild Jelly Bean on top of their hardened microvisor for the "Knox" project.[172][173]

As part of the broader 2013 mass surveillance disclosures it was revealed in September 2013 that the American and British intelligence agencies, the National Security Agency (NSA) and Government Communications Headquarters (GCHQ), respectively, have access to the user data on iPhone, BlackBerry, and Android devices. They are reportedly able to read almost all smartphone information, including SMS, location, emails, and notes.[174] In January 2014, further reports revealed the intelligence agencies' capabilities to intercept the personal information transmitted across the Internet by social networks and other popular applications such as Angry Birds, which collect personal information of their users for advertising and other commercial reasons. GCHQ has, according to The Guardian, a wiki-style guide of different apps and advertising networks, and the different data that can be siphoned from each.[175] Later that week, the Finnish Angry Birds developer Rovio announced that it was reconsidering its relationships with its advertising platforms in the light of these revelations, and called upon the wider industry to do the same.[176]

The documents revealed a further effort by the intelligence agencies to intercept Google Maps searches and queries submitted from Android and other smartphones to collect location information in bulk.[175] The NSA and GCHQ insist their activities are in compliance with all relevant domestic and international laws, although the Guardian stated "the latest disclosures could also add to mounting public concern about how the technology sector collects and uses information, especially for those outside the US, who enjoy fewer privacy protections than Americans."[175]

Licensing

The source code for Android is open source; it is developed in private by Google, with the source code released publicly when a new version of Android is released. Google publishes most of the code (including network and telephony stacks) under the non-copyleftApache License version 2.0. which allows modification and redistribution.[177][178] The license does not grant rights to the "Android" trademark, so device manufacturers and wireless carriers have to license it from Google under individual contracts. Associated Linux kernel changes are released under the copyleftGNU General Public License version 2, developed by the Open Handset Alliance, with the source code publicly available at all times. Typically, Google collaborates with a hardware manufacturer to produce a flagship device (part of the Nexus series) featuring the new version of Android, then makes the source code available after that device has been released.[179] The only Android release which was not immediately made available as source code was the tablet-only 3.0 Honeycomb release. The reason, according to Andy Rubin in an official Android blog post, was because Honeycomb was rushed for production of the Motorola Xoom,[180] and they did not want third parties creating a "really bad user experience" by attempting to put onto smartphones a version of Android intended for tablets.[181]

While all of Android itself is open source software, most Android devices ship with a large amount of proprietary software, such as Google Mobile Services, which includes apps such as Google Play Store, Google Search, and Google Play Services—a software layer which provides APIs that integrate with Google-provided services, among others. These apps must be licensed from Google by device makers, and can only be shipped on devices which meet its compatibility guidelines and other requirements.[59][101] Custom, certified distributions of Android produced by manufacturers (such as TouchWiz and HTC Sense) may also replace certain stock Android apps with their own proprietary variants and add additional software not included in the stock Android operating system.[3] There may also be "binary blob" drivers required for certain hardware components in the device.[3][92]

Several stock apps in Android's open source code used by previous versions (such as Search, Music, and Calendar) have also been effectively deprecated by Google, with development having shifted to newer but proprietary versions distributed and updated through Play Store, such as Google Search and Google Play Music. While these older apps remain in Android's source code, they have no longer received any major updates. Additionally, proprietary variants of the stock Camera and Gallery apps also include certain functions (such as Photosphere panoramas and Google+ album integration) that are excluded from open source versions (however, they have yet to be completely abandoned). Similarly, the Nexus 5 uses a non-free variation of Android 4.4's home screen that is embedded directly within the Google Search app, adding voice-activated search and the ability to access Google Now as a page on the home screen itself. Although an update for Google Search app containing the relevant components was released through Google Play for all Android devices, the new home screen required an additional stub application to function, and was not provided in Android 4.4 updates for any other devices (which still used the existing home screen from Android version 4.3). The stub application was officially released on Play Store as Google Now Launcher in February 2014, initially for Nexus and Google Play Edition devices with Android version 4.4.[3][182][183][184]

Richard Stallman and the Free Software Foundation have been critical of Android and have recommended the usage of alternatives such as Replicant, because drivers and firmware vital for the proper functioning of Android devices are usually proprietary, and because Google Play can forcibly install or deinstall apps and invites non-free software.[185][186]

Leverage over manufacturers

Google licenses their Google Mobile Services software, along with Android trademarks, only to hardware manufacturers for devices that meet Google's compatibility standards specified in the Android Compatibility Program document.[187] Thus, forks of Android that make major changes to the operating system itself do not include any of Google's non-free components, stay incompatible with applications that require them, and must ship with an alternative software marketplace in lieu of Google Play Store.[3] Examples of such Android forks are the Amazon's Fire OS (which is used on the Kindle Fire line of tablets, and oriented toward Amazon services), the Nokia X Software Platform (a fork used by the Nokia X family, oriented primarily toward Nokia and Microsoft services), and other forks that exclude Google apps due to the general unavailability of Google service in that country and licensing fees (such as in China).[188][189] In 2014, Google also began to require that all Android devices which license the Google Mobile Services software display a prominent "Powered by Android" logo on their boot screens.[59]

Members of the Open Handset Alliance, which include the majority of Android OEMs, are also contractually forbidden from producing Android devices based on forks of the OS;[3][190] in 2012, Acer Inc. was forced by Google to halt production on a device powered by Alibaba Group's Aliyun OS with threats of removal from the OHA, as Google deemed the platform to be an incompatible version of Android. Alibaba Group defended the allegations, arguing that the OS was a distinct platform from Android (primarily using HTML5 apps), but incorporated portions of Android's platform to allow backwards compatibility with third-party Android software. Indeed, the devices did ship with an application store which offered Android apps; however, the majority of them were pirated.[191][192][193]

Reception

Android-x86 running on an ASUS EeePC netbook; Android has been unofficially ported to traditional PCs for use as a desktop operating system.

Android received a lukewarm reaction when it was unveiled in 2007. Although analysts were impressed with the respected technology companies that had partnered with Google to form the Open Handset Alliance, it was unclear whether mobile phone manufacturers would be willing to replace their existing operating systems with Android.[194] The idea of an open-source, Linux-based development platform sparked interest,[195] but there were additional worries about Android facing strong competition from established players in the smartphone market, such as Nokia and Microsoft, and rival Linux mobile operating systems that were in development.[196] These established players were skeptical: Nokia was quoted as saying "we don't see this as a threat,"[197] and a member of Microsoft's Windows Mobile team stated "I don't understand the impact that they are going to have."[197]

Since then Android has grown to become the most widely used smartphone operating system[16][198] and "one of the fastest mobile experiences available."[199] Reviewers have highlighted the open-source nature of the operating system as one of its defining strengths, allowing companies such as Nokia (Nokia X family),[200]Amazon (Kindle Fire), Barnes & Noble (Nook), Ouya, Baidu and others to fork the software and release hardware running their own customised version of Android. As a result, it has been described by technology website Ars Technica as "practically the default operating system for launching new hardware" for companies without their own mobile platforms.[16] This openness and flexibility is also present at the level of the end user: Android allows extensive customisation of devices by their owners and apps are freely available from non-Google app stores and third party websites. These have been cited as among the main advantages of Android phones over others.[16][201]

Despite Android's popularity, including an activation rate three times that of iOS, there have been reports that Google has not been able to leverage their other products and web services successfully to turn Android into the money maker that analysts had expected.[202]The Verge suggested that Google is losing control of Android due to the extensive customization and proliferation of non-Google apps and services—Amazon's Kindle Fire line uses Fire OS, a heavily modified fork of Android which does not include or support any of Google's proprietary components, and requires that users obtain software from its competing Amazon Appstore instead of Play Store.[3] In 2014, in an effort to improve prominence of the Android brand, Google began to require that devices featuring its proprietary components display an Android logo on the boot screen.[59]

Android has suffered from "fragmentation",[203] a situation where the variety of Android devices, in terms of both hardware variations and differences in the software running on them, makes the task of developing applications that work consistently across the ecosystem harder than rival platforms such as iOS where hardware and software varies less. For example, according to data from OpenSignal in July 2013, there were 11,868 models of Android device, numerous different screen sizes and eight Android OS versions simultaneously in use, while the large majority of iOS users have upgraded to the latest iteration of that OS.[204] Critics such as Apple Insider have asserted that fragmentation via hardware and software pushed Android's growth through large volumes of low end, budget-priced devices running older versions of Android. They maintain this forces Android developers to write for the "lowest common denominator" to reach as many users as possible, who have too little incentive to make use of the latest hardware or software features only available on a smaller percentage of devices.[205] However, OpenSignal, who develops both Android and iOS apps, concluded that although fragmentation can make development trickier, Android's wider global reach also increases the potential reward.[204]

Market share

Research company Canalys estimated in the second quarter of 2009 that Android had a 2.8% share of worldwide smartphone shipments.[206] By the fourth quarter of 2010 this had grown to 33% of the market, becoming the top-selling smartphone platform,[207] overtaking Symbian.[208] By the third quarter of 2011 Gartner estimated that more than half (52.5%) of the smartphone sales belonged to Android.[209] By the third quarter of 2012 Android had a 75% share of the global smartphone market according to the research firm IDC.[210]

In July 2011, Google said that 550,000 new Android devices were being activated every day,[211] up from 400,000 per day in May,[212] and more than 100 million devices had been activated[213] with 4.4% growth per week.[211] In September 2012, 500 million devices had been activated with 1.3 million activations per day.[214][215] In May 2013, at Google I/O, Sundar Pichai announced that 900 million Android devices had been activated.[216]

Android market share varies by location. In July 2012, "mobile subscribers aged 13+" in the United States using Android were up to 52%,[217] and rose to 90% in China.[218] During the third quarter of 2012, Android's worldwide smartphone shipment market share was 75%,[210] with 750 million devices activated in total. In April 2013 Android had 1.5 million activations per day.[215] As of May 2013[update], 48 billion applications ("apps") have been installed from the Google Play store,[61] and by September 2013, one billion Android devices have been activated.[219]

As of July 2013[update], the Google Play store has had over one million Android applications published, and over 50 billion applications downloaded.[11] A developer survey conducted in April–May 2013 found that Android is used by 71% of mobile developers.[12] The operating system's success has made it a target for patent litigation as part of the so-called "smartphone wars" between technology companies.[18][19]

Android devices account for more than half of smartphone sales in most markets, including the US, while "only in Japan was Apple on top" (September–November 2013 numbers).[220] At the end of 2013, over 1.5 billion Android smartphones have been sold in the four years since 2010,[221][222] making Android the most sold phone and tablet OS. Three billion Android smartphones are estimated to be sold by the end of 2014 (including previous years). According to Gartner research company, Android-based devices outsold all contenders, every year since 2012.[223] In 2013, it outsold Windows 2.8:1 or by 573 million.[224][225][226] Android has the largest installed base of all general-purpose operating systems; as of 2013[update], devices running it also sell more than Windows, iOS and Mac OS X devices combined.

Since July 2014, Android is the most popular mobile operating system when it comes to use for web browsing, according to NetApplications.[227] In India and other countries, Android is the most popular operating system overall (not just counting the "mobile" ones) for web browsing usage. According to StatCounter, "mobile usage has already overtaken desktop in several countries including India, South Africa and Saudi Arabia",[228] with several countries in Africa having done so already, including Ethiopia and Kenya in which mobile usage is at 72.23%.[229]

While Android phones in the west commonly include Google's proprietary add-ons (such as Google Play) to the otherwise open source operating system, increasingly this is not done in emerging markets; "ABI Research claims that 65 million devices shipped globally with open-source Android in the second quarter of [2014], up from 54 million in the first quarter"; depending on country, percent of phones estimated to be based only on Android's source code (AOSP), forgoing the Android trademark: Thailand (44%), Philippines (38%), Indonesia (31%), India (21%), Malaysia (24%), Mexico (18%), Brazil (9%).[230]

According to Gartner, "Android surpassed a billion shipments of devices in 2014, and will continue to grow at a double-digit pace in 2015, with a 26 percent increase year over year." This makes it the first time that any general-purpose operating system has reached more than one billion end users within a year: by reaching close to 1.16 billion end users in 2014, Android shipped over four times more than iOS and OS X combined, and over three times more than Microsoft Windows. Gartner expects the whole mobile phone market to "reach two billion units in 2016", including Android.[231]

By Statistica's estimate, Android smartphones have an installed base, in 2014, of 1600 million Androids smartphones (75% of the estimated 2.2 billion);[232][233] To put the Statistica's numbers in context: by Strategy Analytics estimates, Windows the most popular "desktop" operating system, has an estimated installed base of about 1300 million at best;[234] they also estimate the overall tablet installed base to be already of comparable size to the PC market and predict tablets will have surpassed them by 2018. Most of the tablet installed base consists of Androids that add to the above Android smartphone numbers.[b]

Tablets

Despite its success on smartphones, initially Android tablet adoption was slow.[244] One of the main causes was the chicken or the egg situation where consumers were hesitant to buy an Android tablet due to a lack of high quality tablet applications, but developers were hesitant to spend time and resources developing tablet applications until there was a significant market for them.[245][246] The content and app "ecosystem" proved more important than hardware specs as the selling point for tablets. Due to the lack of Android tablet-specific applications in 2011, early Android tablets had to make do with existing smartphone applications that were ill-suited to larger screen sizes, whereas the dominance of Apple's iPad was reinforced by the large number of tablet-specific iOS applications.[246][247]

Despite app support in its infancy, a considerable number of Android tablets (alongside those using other operating systems, such as the HP TouchPad and BlackBerry PlayBook) were rushed out to market in an attempt to capitalize on the success of the iPad.[246]InfoWorld has suggested that some Android manufacturers initially treated their first tablets as a "Frankenphone business", a short-term low-investment opportunity by placing a smartphone-optimized Android OS (before Android 3.0 Honeycomb for tablets was available) on a device while neglecting user interface. This approach, such as with the Dell Streak, failed to gain market traction with consumers as well as damaging the early reputation of Android tablets.[248][249] Furthermore, several Android tablets such as the Motorola Xoom were priced the same or higher than the iPad, which hurt sales. An exception was the AmazonKindle Fire, which relied upon lower pricing as well as access to Amazon's ecosystem of applications and content.[246][250]

This began to change in 2012 with the release of the affordable Nexus 7 and a push by Google for developers to write better tablet applications.[251] According to International Data Corporation, shipments of Android-powered tablets surpassed iPads in Q3 2012.[252]

As of the end of 2013, over 191.6 million Android tablets had sold in three years since 2011.[253][254] This made Android tablets the most-sold type of tablet in 2013, surpassing iPads in the second quarter of 2013.[255]

As of March 2015[update], according to StatCounter and by accounting Android tablets accessing the web—​a proxy for their installed base—​they are catching up to the iPad in big countries and continents such as South America, having done so already in Russia (51%),[256] India (63.25%),[257] Indonesia (62.22%),[258] and the whole Africa (53%).[259] China is a major exception for big developing countries, in which Android phablets (classified as smartphones, while similar to tablets, an in-between size) are however much more popular than Android tablets or iPads.

Desktops and laptops

Android comes preinstalled on some laptops and can also be installed on most personal computers by end users. One reviewer commented:

“

You can even Alt-Tab between running applications, something you don’t really notice until you use Android on a laptop or desktop.

The notification center is vastly more complete and robust than in most environments. Just about every type of notification comes through this one user interface, functionality that other desktops only dream of. [..]

If one can get over the whole “every app runs full screen” shebang, Android actually makes for an astoundingly usable, easy to learn, fairly peppy and relatively good-looking desktop environment.

Would I enjoy the Android user experience as my primary Linux Desktop experience? Yes. Absolutely. In fact, for long periods of time, Android has been my primary computing platform. And the environment is absolutely usable for that purpose.

Bryan also notes that "Photoshop for Android tablets [..] runs remarkably well on an Android laptop."[261]

Platform usage

Lollipop (3.3%)

KitKat (40.9%)

Jelly Bean (42.6%)

Ice Cream Sandwich (5.9%)

Gingerbread (6.9%)

Froyo (0.4%)

Charts in this section provide breakdowns of Android versions, based on the devices accessing the Play Store in a seven-day period ending on March 2, 2015.[262][c] Therefore, these statistics exclude Android forks that do not access Google Play, such as Amazon's Fire tablets.

Application piracy

In general, paid Android applications can easily be pirated.[263] In a May 2012 interview with Eurogamer, the developers of Football Manager stated that the ratio of pirated players vs legitimate players was 9:1 for their game Football Manager Handheld.[264] However, not every developer agreed that piracy rates were an issue; for example, in July 2012 the developers of the game Wind-up Knight said that piracy levels of their game were only 12%, and most of the piracy came from China, where people cannot purchase apps from Google Play.[265]

In 2010, Google released a tool for validating authorized purchases for use within apps, but developers complained that this was insufficient and trivial to crack. Google responded that the tool, especially its initial release, was intended as a sample framework for developers to modify and build upon depending on their needs, not as a finished piracy solution.[266] In 2012 Google released a feature in Android 4.1 that encrypted paid applications so that they would only work on the device on which they were originally installed from the Google Play Store, but this feature has been temporarily deactivated due to technical issues.[267]

Legal issues

Both Android and Android phone manufacturers have been involved in numerous patent lawsuits. On August 12, 2010, Oracle sued Google over claimed infringement of copyrights and patents related to the Java programming language.[268] Oracle originally sought damages up to $6.1 billion,[269] but this valuation was rejected by a United States federal judge who asked Oracle to revise the estimate.[270] In response, Google submitted multiple lines of defense, counterclaiming that Android did not infringe on Oracle's patents or copyright, that Oracle's patents were invalid, and several other defenses. They said that Android is based on Apache Harmony, a clean room implementation of the Java class libraries, and an independently developed virtual machine called Dalvik.[271] In May 2012, the jury in this case found that Google did not infringe on Oracle's patents, and the trial judge ruled that the structure of the Java APIs used by Google was not copyrightable.[272][273] The parties agreed to zero dollars in statutory damages for a small amount of copied code.[274] On May 9, 2014, the Federal Circuit partially reversed the district court ruling, ruling in Oracle's favor on the copyrightability issue, and remanding the issue of fair use to the district court.[275][276]

In addition to lawsuits against Google directly, various proxy wars have been waged against Android indirectly by targeting manufacturers of Android devices, with the effect of discouraging manufacturers from adopting the platform by increasing the costs of bringing an Android device to market.[277] Both Apple and Microsoft have sued several manufacturers for patent infringement, with Apple's ongoing legal action against Samsung being a particularly high-profile case. In October 2011, Microsoft said they had signed patent license agreements with ten Android device manufacturers, whose products account for "70% in the U.S.". and 55% of the worldwide revenue for Android devices.[278] These include Samsung and HTC.[279] Samsung's patent settlement with Microsoft includes an agreement that Samsung will allocate more resources to developing and marketing phones running Microsoft's Windows Phone operating system.[277]

Google has publicly expressed its frustration for the current patent landscape in the United States, accusing Apple, Oracle and Microsoft of trying to take down Android through patent litigation, rather than innovating and competing with better products and services.[280] In 2011–12, Google purchased Motorola Mobility for US$12.5 billion, which was viewed in part as a defensive measure to protect Android, since Motorola Mobility held more than 17,000 patents.[281] In December 2011, Google bought over a thousand patents from IBM.[282]

In 2011, Google demonstrated "Android@Home", a home automation technology which uses Android to control a range of household devices including light switches, power sockets and thermostats.[296] Prototype light bulbs were announced that could be controlled from an Android phone or tablet, but Android head Andy Rubin was cautious to note that "turning a lightbulb on and off is nothing new", pointing to numerous failed home automation services. Google, he said, was thinking more ambitiously and the intention was to use their position as a cloud services provider to bring Google products into customers' homes.[297][298]

On March 18, 2014, Google announced Android Wear, an Android-based platform specifically intended for smartwatches and other wearable devices; only a developer preview was made publicly available.[303] This was followed by the unveiling of two Android Wear–based devices, the LG G Watch and Moto 360.[304]

Notes

^Official 64-bit support for all platforms was introduced in Android 5.0 "Lollipop".

^Android has the largest installed base of any mobile operating system and, as of 2013[update], the highest-selling operating system overall. Android devices sell more than Microsoft Windows, iOS, and Mac OS X devices combined,[224][235][236][237][238] with sales in 2012, 2013 and 2014[239] close to the installed base of all PCs.[240] In the third quarter of 2013, Android's share of the global smartphone shipment market was 81.3%, the highest ever,[241] and the Android share—​led by Samsung products—​was 81.3%;[241][242][243] During this time period over 261 million smartphones were sold globally, with around 211 million of those running Android.[242]

^Provided numbers give a slightly inaccurate distribution of APIs. For example, information about the Amazon Appstore would only show a subset of the APIs/versions, that is, those used by Amazon's products.

^"Licenses". Android Open Source Project. Open Handset Alliance. Retrieved September 9, 2012. The preferred license for the Android Open Source Project is the Apache Software License, 2.0. ... Why Apache Software License? ... For userspace (that is, non-kernel) software, we do in fact prefer ASL2.0 (and similar licenses like BSD, MIT, etc.) over other licenses such as LGPL. Android is about freedom and choice. The purpose of Android is promote openness in the mobile world, but we don't believe it's possible to predict or dictate all the uses to which people will want to put our software. So, while we encourage everyone to make devices that are open and modifiable, we don't believe it is our place to force them to do so. Using LGPL libraries would often force them to do so.

^ abcdefElgin, Ben (August 17, 2005). "Google Buys Android for Its Mobile Arsenal". Bloomberg Businessweek. Bloomberg. Archived from the original on February 24, 2011. Retrieved February 20, 2012. In what could be a key move in its nascent wireless strategy, Google (GOOG) has quietly acquired startup Android, Inc., ...

^ abGreg Kroah-Hartman (February 2, 2010). "Android and the Linux kernel community". Retrieved February 20, 2012. Google shows no sign of working to get their code upstream anymore. Some companies are trying to strip the Android-specific interfaces from their codebase and push that upstream, but that causes a much larger engineering effort, and is a pain that just should not be necessary.